Summary: Facial clefts are one of the most common birth defects, affecting 2 out of every thousand babies. While the main causes of facial clefts are unknown, it is obvious that genetics plays a strong role. We?ve shown that families with one member affected by clefts are 40 times as likely to have a baby with a cleft. Environmental factors are also presumed to play a role in clefts. For example, clefts are easily produced in experimental animals exposed to teratogens. It is very plausible that humans vary in their genetic susceptibility to teratogens that cause clefts. More than a decade ago, we anticipated that genetic susceptibility would become an important area of epidemiologic research at NIEHS. Accordingly, we selected facial clefts as a condition with both genetic and environmental causes, and we began in 1992 to develop a study to address the causes of clefts. In 1996 we launched a population-based case-control study of facial clefts in Norway. (Norway has one of the highest rates of cleft lip and palate in the world.) The field phase was completed in 2002. We enrolled 90% of all babies with facial clefts born in Norway between 1996 and 2002 (600 cases), and 800 control infants selected randomly from the population. Mothers of these infants provided detailed information on occupational and other exposures during pregnancy, as well as on nutrition, personal habits and medical history. Biological samples for DNA analysis were collected from cases and controls as well as their mothers, fathers and siblings. These total nearly 4000 people. DNA has been extracted from these samples and is now ready for genetic analysis. In the course of carrying out this study, we developed and published a new statistical strategy for the analysis of genetic data in case-parent triads that has been widely adapted. We have demonstrated the application of this new method in a preliminary analysis of 262 case-parent triads (see this year?s publications). However, the main analyses are still to come. Last year's progress: - Completion of field study and cleaning of the questionnaire data - Preliminary analysis of genetic and exposure data for 262 case-parent triads Our preliminary analysis of 262 case-parent triads explored a group of developmental genes (TGFA, TGFB3, and MSX1) that have been reported as being associated with facial clefts. We did not find these genes to be strongly associated with clefts, although there was evidence of a gene-gene interaction between the TGFA TaqI A2 allele and the MSX-1-CA allele. This remains to be confirmed in our larger study. Two previous studies had suggested that these genes interact with maternal cigarette smoking to produce clefts. We did not see interactions of smoking or other exposures with these gene alleles in our data. Finally, we explored the association of vitamin-metabolizing genes with clefts. Previous studies have suggested the possibility that folic acid might protect against clefting. The gene MTHFR regulates a key step in metabolism of folate. We found evidence that allelic variants of the MTHFR gene are associated with the risk of both cleft lip and cleft palate. We will explore these associations more definitively in the larger study, taking into account also the dietary consumption of folate and the use of vitamins containing folic acid.